Imageable elements, such as lithographic printing form precursors, electronic part precursors and mask precursors typically are formed by coating a film-forming, radiation absorbing compound on to a substrate. Conventional radiation absorbing compounds include photosensitive components dispersed within a polymeric binder. After a portion of the radiation absorbing compound is exposed (commonly referred to as imagewise exposure), the exposed portion becomes either more soluble or less soluble in a developer than an unexposed portion of the radiation absorbing compound. In a positive working imageable element, the exposed regions of the radiation absorbing compound become more soluble in a developer than non-exposed regions. Conversely, in a negative working plate, the exposed regions become less soluble in a developer than non-exposed regions. In each instance, it is the undeveloped areas that remain on the plate, while the developed regions reveal the substrate's hydrophilic surface.
Radiation absorbing compounds that respond to infrared (IR) radiation have recently become of interest. In these systems, the radiation absorbing compounds contain IR absorbers that convert IR radiation to heat. A suitable IR radiation source is an IR laser digitally controlled to produce the required pattern of irradiated or heated areas. These compositions are suitable for advanced “Computer-to-Plate” (CTP) techniques. Some IR compositions, which are not sensitive to ultra-violet or visible radiation, offer the advantage of not needing to be handled in a dark room, or under ultra-violet safelighting conditions. Rather, these compositions can be handled in ordinary light.
The radiation absorbing compounds must balance several properties needed for imaging. These properties include suitable adhesion to the substrate, suitable development after imaging, and suitable resolution. Two approaches have been pursued to reach a proper balance of properties in these materials. The first approach concentrates on improving the quality of the photosensitive components of the materials. The second approach involves improving the quality of the polymeric binder that controls the physical and mechanical properties of the material. The second approach has been the source of significant research and innovation because the behavior of the radiation absorbing compound in the imaging, developing and printing processes, as well as the shelf life and durability of the imageable element are related to the choice of binder material.
Some IR absorbing compounds have suitable adherence to substrates. Other IR absorbing compounds exhibit suitable photosensitivity under conventional imaging conditions. Still other IR absorbing compounds are able to withstand the extended exposure and development steps required in the productions of certain imageable elements, particularly printing plates. Other IR absorbing compounds have sufficient developer resistance after imaging. Further yet, certain polymer binders have suitable resistance to the mechanical stress that imageable elements are subjected to, as well as chemicals used to clean and treat finished plates. Nonetheless, an IR absorbing compound that exhibits all of these properties is currently the focus of ongoing research.